Urethane (meth)acrylate oligomer, process for its production and photo-curable composition

ABSTRACT

A urethane (meth)acrylate oligomer which has a low viscosity and gives a flexible cured product having a low surface tackiness, is provided. It is obtainable by reacting a polyol component comprising a polyoxyalkylene polyol which has from 2 to 4 hydroxyl groups, a hydroxyl value V OH  (mgKOH/g) of from 5 to 115 and a total degree of unsaturation V US  (meq/g) satisfying V US ≦(0.45/V OH )+0.02, with a polyisocyanate compound and a hydroxylated (meth)acrylate compound.

TECHNICAL FIELD

[0001] The present invention relates to a urethane (meth)acrylateoligomer, a process for its production and a photo-curable composition.Particularly, it relates to a urethane (meth)acrylate oligomer which hasa low viscosity and which gives a cured product excellent in flexibilityand adhesive property and having a low surface stickiness (hereinafterreferred to as a surface tackiness), a process for its production and aphoto-curable composition containing such an oligomer.

BACKGROUND ART

[0002] In recent years, in all technical fields, energy saving, resourcesaving and environmental measures have become important subjects, andvarious technical developments have been made. As one of them, aphoto-curable resin composition has been developed and used inapplications to e.g. coating materials, adhesives, coating agents,printing ink vehicles, resist inks, relief printing plate materials,optical fiber coating materials and optical shaping materials. Such aphoto-curable resin composition comprises a photo-curable oligomer, aphoto-polymerizable monomer, a photo-polymerization initiator, asensitizer, a colorant and other additives and contains substantially novolatile solvent, and it undergoes a curing reaction by irradiation withlight rays having a certain specific wavelength to give a cured productexcellent in flexibility and adhesive properties.

[0003] The photo-curable oligomer to be used here, is usually one havingfrom one to several (meth)acryloyl groups as photo-curable functionalgroups in .its molecular structure. Among such oligomers, a urethane(meth)acrylate oligomer obtainable by reacting a polyol and apolyisocyanate compound, is used in a wide range of fields, as its curedproduct exhibits excellent performance in the toughness, hardness,chemical resistance, flexibility, adhesive property, light resistance,low temperature characteristics, etc.

[0004] With respect to such a urethane (meth)acrylate oligomer,molecular designing can easily be done by changing the starting materialvariously depending upon the particularly purpose of its use.Especially, it is easy to change the performance by the polyol to beused. When a low molecular weight polyol having a molecular weight ofabout a few hundreds, is used, a hard and brittle cured product will beobtained, and when a high molecular weight polyol having a molecularweight of from a thousand to a few thousands, is employed, a flexibleand tough cured product will be obtained. As such a high molecularweight polyol, a polyoxyalkylene polyol, a polyester polyol, apolycaprolactone polyol or a polycarbonate polyol is, for example,employed.

[0005] However, if a high molecular weight polyol is used, the viscosityof the resulting urethane (meth)acrylate oligomer will be high, and ithas been difficult to let the urethane moiety have a high molecularweight so as to obtain sufficient flexibility. Further, because of thehigh viscosity, there has been a problem in working efficiency, and asshown in JP-A-9-48830, it used to be necessary to employ a low molecularweight (meth)acrylate compound as a viscosity-reducing agent.

[0006] As a low viscosity polyol, a polyoxyalkylene polyol is known.However, if a common polyoxyalkylene polyol as shown in JP-A-10-95640 isused, since such a polyol contains a substantial amount of a by-productmonool, the curing tends to be slow, and there has been a problem thatno adequate physical properties can be obtained, or the surfacetackiness of the cured product remains.

[0007] Under these circumstances, the present inventors have conductedan extensive study, and as a result, have found it possible to obtain aphoto-curable composition which has a low viscosity and excellentcurability and which gives a cured product having little surfacetackiness, by employing a certain specific urethane (meth)acrylateoligomer based on a polyoxyalkylene polyol having a low total degree ofunsaturation (i.e. a small monool content). The present invention hasbeen accomplished on the basis of this discovery.

DISCLOSURE OF THE INVENTION

[0008] The present invention has been made to solve the above-mentionedproblems. In the first aspect, the present invention provides a urethane(meth)acrylate oligomer obtainable by reacting a polyol component (A)comprising a polyoxyalkylene polyol which has from 2 to 4 hydroxylgroups, a hydroxyl value V_(OH) (mgKOH/g) of from 5 to 115 and a totaldegree of unsaturation V_(US) (meq/g) satisfying the formula 1, with apolyisocyanate compound (B) and a hydroxylated (meth)acrylate compound(C):

V _(US)≦(0.45/V _(OH))+0.02  Formula 1

[0009] In the second aspect, the present invention further provides aphoto-curable composition comprising the above urethane (meth)acrylateoligomer and a photo-polymerization initiator.

[0010] In this specification, “(meth)acrylate” is used as a general termrepresenting “acrylate” and “methacrylate”.

BEST MODE FOR CARRYING OUT THE INVENTION

[0011] The polyoxyalkylene polyol which has from 2 to 4 hydroxyl groups,a hydroxyl value V_(OH) (mgKOH/g) of from 5 to 115 and a total degree ofunsaturation V_(US) (meq/g) satisfying the formula 1, to be used in thepresent invention, can be obtained usually by employing diethyl zinc,iron chloride, metal porphyrin, a double metal cyanide complex, a cesiumcompound or the like, as a catalyst. Especially preferred is oneobtained by using a double metal cyanide complex. In the case of acommonly employed alkali metal such as potassium hydroxide, theunsaturated degree tends to be high especially with a high molecularweight product, such being undesirable.

[0012] The double metal cyanide complex may preferably be a complexcomprising zinc hexacyanocobaltate as the main component, particularlypreferably its ether and/or alcohol complex. As its composition, onedisclosed in JP-B-46-27250 can essentially be employed. As the ether, anethylene glycol dimethyl ether (glyme) or a diethylene glycol dimethylether (diglyme) may, for example, be preferred, and particularlypreferred is glyme from the handling efficiency for the production ofthe complex. As the alcohol, t-butanol or t-butylcellosolve may, forexample, be preferred.

[0013] The polyoxyalkylene polyol in the present invention, is producedby reacting a polyfunctional initiator with a monoepoxide in thepresence of the above-mentioned catalyst. The monoepoxide is a compoundhaving one epoxy ring, such as an alkylene oxide, glycidyl ether orglycidyl ester. As a preferred monoepoxide, ethylene oxide, propyleneoxide, 1,2-butylene oxide, 2,3-butylene oxide, or styrene oxide may bementioned. Particularly preferred is ethylene oxide or propylene oxide.These monoepoxides may be used in combination as a mixture of two ormore of them.

[0014] The number of hydroxyl groups of such a polyoxyalkylene polyol isfrom 2 to 4, preferably from 2 to 3. Namely, as the initiator, acompound having from 2 to 4 active hydrogen atoms, is used. As theinitiator, a polyhydroxy compound having from 2 to 4 hydroxyl groups ispreferred, and particularly preferred is a polyhydroxy compound havingfrom 2 to 3 hydroxyl groups. Specifically, ethylene glycol, diethyleneglycol, propylene glycol, dipropylene glycol, neopentyl glycol,1,4-butandiol, 1,6-hexane diol, glycerol, trimethylol propane,pentaerythritol, and a polyol having a molecular weight lower than thedesired product, obtained by reacting an alkylene oxide thereto, may bementioned. These polyhydroxy compounds may be used alone or incombination as a mixture of two or more of them. The hydroxyl valueV_(OH) (mgKOH/g) of the polyoxyalkylene polyol is from 5 to 115,preferably from 7 to 80, more preferably from 9 to 30. With a hydroxylvalue higher than this, no adequate flexibility can be obtained, andwith a lower hydroxyl value, no adequate strength will be obtained. Thetotal degree of unsaturation V_(US) (meq/g) of the polyoxyalkylenepolyol is required to satisfy the formula 1 relating to the hydroxylvalue V_(OH) (mgKOH/g), preferably satisfies the formula 2, morepreferably satisfies the formula 3.

V _(US)≦(0.45/V _(OH))+0.02  Formula 1

V _(US)≦(0.45/V _(OH))+0.01  Formula 2

V _(US)≦(0.45/V _(OH))  Formula 3

[0015] If the total degree of unsaturation is higher than this, anincrease in the surface tackiness of the cured product or a decrease inthe curing property, are observed, such being undesirable.

[0016] As the polyol component (A) in the present invention, theabove-mentioned polyoxyalkylene alkylene polyol is mainly used, but insome cases, it may be used in combination with other polyoxyalkylenepolyols.

[0017] The polyisocyanate compound (B) in the present invention may bean aromatic, aliphatic or aromatic ring-containing aliphatic isocyanatehaving at least two isocyanate groups on average, or an isocyanate ofmodified polyisocyanate type obtained by modification thereof.

[0018] Specifically, it may be a polyisocyanate such as tolylenediisocyanate, diphenylmethane diisocyanate, polymethylenepolyphenyleneisocyanate (crude MDI), xylylene diisocyanate, isophorone diisocyanateor hexamethylene diisocyanate, or its prepolymer-modified product,nulate-modified product, urea-modified product or carbodiimide modifiedproduct. Among them, a diisocyanate having two isocyanate groups in onemolecule, is preferred. These polyisocyanate compounds may be used aloneor in combination as a mixture of two or more of them.

[0019] The hydroxylated (meth)acrylate compound (C) in the presentinvention may preferably be a hydroxyalkyl (meth)acrylate wherein thecarbon number of the alkyl group moiety is from 1to 10, particularlypreferably a hydroxyalkyl (meth)acrylate wherein the carbon number ofthe alkyl group moiety is from 1 to 5. Particularly preferred among themis a hydroxyalkyl acrylate. Specifically, 2-hydroxyethyl (meth)acrylate,2-hydroxypropyl (meth)acrylate, 3-hydroxypropyl (meth)acrylate,2-hydroxybutyl (meth)acrylate, 4-hydroxybutyl (meth)acrylate, pentandiolmono(meth)acrylate or hexanediol mono(meth)acrylate may, for example, bementioned, and 2-hydroxyethyl (meth)acrylate or 2-hydroxypropyl(meth)acrylate is particularly preferred. 2-Hydroxyethyl acrylate or2-hydroxypropyl acrylate is most preferred. These hydroxylated(meth)acrylate compounds may be used alone or in combination as amixture of two or more of them.

[0020] The present invention provides a process for producing a urethane(meth)acrylate oligomer, which comprises reacting the above-mentionedpolyol component (A), the polyisocyanate compound (B) and thehydroxylated (meth)acrylate compound (C). Specifically, the followingmethods (1) to (3) may be mentioned.

[0021] (1) A method in which the polyol component (A), thepolyisocyanate compound (B) and the hydroxylated (meth)acrylate compound(C) are reacted simultaneously.

[0022] (2) A method wherein the polyisocyanate compound (B) of theformula 2 and the hydroxylated (meth)acrylate compound (C) are reactedunder such a condition that the isocyanate group is stoichiometricallyexcessive, and the obtained reaction product is further reacted with thepolyol component (A).

[0023] (3) A method wherein the polyol component (A) and thepolyisocyanate compound (B) are reacted under such a condition that theisocyanate group is stoichiometrically excessive, and the obtainedreaction product is further reacted with the hydroxylated (meth)acrylatecompound (C).

[0024] In the present invention, the method (3) is particularlypreferred. Namely, particularly preferred is a method in which thepolyol component (A) containing a polyoxyalkylene polyol, and thepolyisocyanate compound (B) are reacted under such a condition that theisocyanate group is stoichiometrically excessive, to obtain a urethaneprepolymer having a terminal isocyanate group, and then the hydroxylated(meth)acrylate compound (C) is reacted to the terminal isocyanate groupof the urethane prepolymer.

[0025] At that time, the proportions of the polyol component (A) and thepolyisocyanate compound (B) are preferably such that the molar ratio ofthe isocyanate group : the hydroxyl group is from 1.3:1 to 3:1, morepreferably from 1.5:1 to 2:1.

[0026] The reaction is preferably carried out at a temperature for acommon urethane-modification reaction i.e. from 30 to 90° C. At the timeof the reaction, a urethane-modification catalyst such as cobaltnaphthenate, zinc naphthenate, lead 2-ethylhexanoate, dibutyltindilaurate, tin 2-ethylhaxanoate, triethylamine or1,4-diazabicyclo[2.2.2]octane, may be used.

[0027] The reaction of the urethane prepolymer having a terminalisocyanate group with the hydroxylated (meth)acrylate compound (C) iscarried out preferably in such a proportion that the molar ratio of theterminal isocyanate group to the hydroxyl group will be from 1:1 to1:1.5. The temperature for the reaction is preferably from 30 to 90° C.At the time of the reaction, a polymerization inhibitor may be added inorder to control the thermal polymerization reaction of the(meth)acryloyl group. As a preferred polymerization inhibitor,hydroquinone, hydroquinone monomethyl ether or o-nitrotoluene, may, forexample, be mentioned. Such a polymerization inhibitor is used within arange of from 50 to 5,000 ppm relative to the hydroxylated(meth)acrylate compound (C).

[0028] In the second aspect, the present invention provides aphoto-curable composition comprising the urethane (meth)acrylateoligomer obtainable as described above, and a photo-polymerizationinitiator.

[0029] The photo-polymerization initiator is not particularly limited,so long as it is one which can be used for conventional photo-curablecompositions, and for example, benzophenone, 4-chlorobenzophenone,4,4′-dimethoxybenzophenone, 4,4′-diaminobenzophenone, acetophenone,3-methylacetophenone, benzoine, benzoine isobutyl ether, benzoineisopropyl ether, benzoine ethyl ether, anthraquinone,1-hydroxycyclohexylphenyl ketone or2-hydroxy-2-methyl-1-phenylpropan-1-one, may be mentioned.

[0030] Such a photo-polymerization initiator can be used within a rangeof from 0.1 to 10 parts by weight, preferably within a range of from 1to 5 parts by weight, per 100 parts by total weight of the urethane.(meth)acrylate oligomer.

[0031] For the purpose of adjusting the physical properties of theresulting cured product, the composition of the present invention maycontain, in addition to the above-mentioned urethane (meth)acrylateoligomer, a urethane (meth)acrylate oligomer obtainable from a polyolother than the polyol component specified in the present invention. Assuch a polyol, polyoxytetramethylene polyol, polyester polyol,polycaprolactone polyol, polycarbonate polyol or polybutadiene polyol,may, for example, be mentioned.

[0032] Further, for the composition of the present invention, for thepurpose of lowering the viscosity, the following ethylenicallyunsaturated group-containing compound may be used as a diluting agent.As such an ethylenically unsaturated group-containing compound, inaddition to the above-mentioned hydroxylated (meth)acrylate compound (C)such as 2-hydroxyethyl (meth)acrylate, a (meth)acrylate compoundcontaining no hydroxyl group, such as an alkyl (meth)acrylate such asmethyl (meth)acrylate or ethyl (meth)acrylate, phenoxyethyl(meth)acrylate or isobonyl (meth)acrylate, or a vinyl ether monomer suchas hydroxybutyl vinyl ether, lauryl vinyl ether or 2-ethylhexyl vinylether, may be mentioned. The urethane (meth)acrylate oligomer of thepresent invention has a low viscosity by itself, and in many cases, sucha diluting agent may not be required. It is preferred not to use such adiluting agent.

[0033] The photo-curable composition of the present invention is used inapplications to e.g. coating materials, adhesives, coating agents,printing ink vehicles, resist inks, relief printing-plate materials,optical fiber coating materials and optical shaping materials, and itcan be photo-cured to provide a cured product which has flexibility andlittle surface tackiness.

EXAMPLES

[0034] Now, the present invention will be described-in detail withreference to Examples (Examples 1 to 4) and Comparative Examples(Comparative Examples 5 and 6), but the present invention is by no meansrestricted to such Examples.

[0035] Preparation of a Polyoxyalkylene Polyol

[0036] Polyol A, C: Prepared by reacting propylene oxide to an initiator(a polyoxypropylene diol having a molecular weight of 700) using zinchexacyanocobaltate-glyme complex as a catalyst, and then, deactivatingthe catalyst, followed by purification.

[0037] Polyol B: One prepared by reacting propylene oxide to aninitiator (a polyoxypropylene diol having a molecular weight of 700)using zinc hexacyanocobaltate-glyme complex as a catalyst, then reactingethylene oxide, then deactivating the catalyst, followed bypurification. The oxyethylene group-content is 20 wt %.

[0038] Polyol D: Prepared by reacting propylene oxide to an initiator (apolyoxypropylene triol having a molecular weight of 1,000) using zinchexacyanocobaltate-glyme complex as a catalyst, then deactivating thecatalyst, followed by purification.

[0039] Polyol E: Prepared by reacting propylene oxide to an initiator (apolyoxypropylene diol having a molecular weight of 700) zinchexacyanocobaltate-t-butanol complex as a catalyst, then deactivatingthe catalyst, followed by purification.

[0040] Polyol F: Prepared by reacting propylene oxide to an initiator (apolyoxypropylene diol having a molecular weight of 700) using potassiumhydroxide as a catalyst, followed by purification. In Table 1, thenumber of hydroxyl groups, the hydroxyl values V_(OH) (mgKOH/g), thetotal degrees of unsaturation V_(US) (meq/g) and values x(x=(0.45/V_(OH))+0.02) are shown. TABLE 1 Total degree of Hydroxyl groupHydroxyl value unsaturation x Polyol A 2 28 0.026 0.036 Polyol B 2 280.018 0.036 Polyol C 2 11 0.034 0.061 Polyol D 3 17 0.029 0.046 Polyol E2 28 0.006 0.036 Polyol F 2 28 0.124 0.036

[0041] Preparation of a urethane acrylate oligomer

Example 1

[0042] To 100 parts by weight (hereinafter referred to simply as parts)(0.025 mol) of polyol A, 8.7 parts (0.05 mol) of tolylene diisocyanate(T-100, tradename, manufactured by Nippon Polyurethane Industry Co.,Ltd.) was added, followed by a reaction at 80° C. for 4 hours in thepresence of 0.01 part of dibutyltin dilaurate, to obtain a urethaneprepolymer. To this urethane prepolymer, 0.05 part of dibutyltindilaurate and 0.05 part of hydroquinone monomethyl ether were added, and6.38 parts (0.055 mol) of 2-hydroxyethyl acrylate was dropwise added at40° C. Thereafter, a reaction was carried out at 60° C. until absorptionby an isocyanate group at a wavelength of 2,250 cm⁻¹ in the infraredabsorption spectrum was no longer observed, to obtain a urethaneacrylate oligomer.

Example 2

[0043] A urethane acrylate oligomer was obtained in the same manner asin Example 1 except that polyol B was used instead of polyol A..

Example 3

[0044] A urethane acrylate oligomer was obtained in- the same manner asin Example 1 except that instead of 100 parts of polyol A, a mixturecomprising 182 parts (0.0182 mol) of polyol C and 45 parts (0.0045 mol)of polyol D, was used, to obtain a-urethane acrylate oligomer.

Example 4

[0045] A urethane acrylate oligomer was obtained in the same manner asin Example 1 except that instead of polyol A, polyol E was used.

Example 5

[0046] A urethane acrylate oligomer was obtained in the same manner asin Example 1 except that instead of polyol A, polyo.1 F was used.

Example 6

[0047] A urethane acrylate oligomer was obtained in the same manner asin Example 1 except that instead of 100 parts of polyol A, 50 parts(0.025 mol) of polyoxytetramethylene glycol having a molecular weight of2,000, was used, to obtain a urethane acrylate oligomer.

[0048] Evaluation

[0049] Examples 1 to 6 were evaluated by the following methods. Theresults are shown in Table 2.

[0050] Viscosity

[0051] The viscosity (cP) at 25° C. was measured by means of an E-typerotary viscometer.

[0052] Surface Tacking and Mechanical Properties of a Cured Product

[0053] To 100 parts of the urethane acrylate oligomer in each ofExamples 1 to 6, 3 parts of benzophenone and 1 part of2-hydroxy-2-methyl-1-phenylpropan-1-one were added and thoroughly mixedat 60° C., to obtain a photo-curable composition. The obtainedphoto-curable composition was coated on an OPP film (Orientedpolypropylene film) bonded to a glass plate by means of an applicator of8 mil and irradiated for 5 seconds by a high pressure mercury lamphaving an output of 80 W/cm from a height of 15 cm, to obtain a curedfilm.

[0054] The surface tackiness of the cured film was evaluated by touchingwith a finger. Evaluation of the surface tackiness was made based on thefollowing standards. ⊚: No tackiness, ◯: no substantial tackiness, Δ:slight tackiness, and X: substantial tackiness.

[0055] Further, the mechanical properties of the film i.e. the tensilestrength (unit: kg/cm²) and the break elongation (unit: %), weremeasured in accordance with JIS K6301. TABLE 2 Mechanical propertiesSurface Tensile Break Example Viscosity tackiness strength elongation 15400 ◯ 55 370 2 5900 ◯ − ⊚ 68 420 3 8200 Δ − ◯ 43 560 4 5600 ⊚ 74 320 54800 X 22 690 6 28000 ⊚ 97 210

[0056] Industrial Applicability

[0057] The urethane (meth)acrylate oligomer employing a polyoxyalkylenepolyol having a low total degree of unsaturation, according to thepresent invention, has a low viscosity as compared with one employingother polyols, and its photo-cured product is excellent in flexibilityand exhibits a remarkable effect such that the surface tackiness is lowas compared with one employing a conventional polyoxyalkylene polyolhaving a high total degree of unsaturation.

[0058] The entire disclosure of Japanese Patent Application No.11-164188 filed on Jun. 10, 1999 including specification, claims andsummary are incorporated herein by reference in its entirety.

What is claimed is:
 1. A urethane (meth)acrylate oligomer obtainable byreacting a polyol component (A) comprising a polyoxyalkylene polyolwhich has from 2 to 4 hydroxyl groups, a hydroxyl value V_(OH) (mgKOH/g)of from 5 to 115 and a total degree of unsaturation V_(US) (meq/g)satisfying the formula 1, with a polyisocyanate compound (B) and ahydroxylated (meth)acrylate compound (C): V _(US)≦(0.45/V_(OH))+0.02  Formula 1
 2. The oligomer according to claim 1, wherein thepolyoxyalkylene-polyol is a polyoxyalkylene polyol obtainable byreacting an alkylene oxide to an initiator by means of a double metalcyanide complex as a catalyst.
 3. A process for producing a urethane(meth)acrylate oligomer, which comprises reacting a polyol component (A)comprising a polyoxyalkylene polyol which has from 2 to 4 hydroxylgroups, a hydroxyl value V_(OH) (mgKOH/g) of from 5 to 115 and a totaldegree of unsaturation V_(US) (meq/g) satisfying the formula 1, with apolyisocyanate compound (B) and a hydroxylated (meth)acrylate compound(C): V _(US)≦(0.45/V _(OH))+0.02  Formula 1
 4. The process for producingthe oligomer according to claim 3, wherein the polyol component (A) andthe polyisocyanate compound (B) are reacted under such a condition thatthe isocyanate group is stoichiometrically excessive, and then, theobtained reaction product is reacted with the hydroxylated(meth)acrylate compound (C).
 5. A photo-curable composition comprisingthe oligomer as defined in claim 1 and a photo-polymerization initiator.